Medically Important Parasites Overview

Medically Important Parasites

• Parasites are eukaryotes that exist in two forms: single-celled protozoa and multicellular helminths (worms).
• Protozoa are subdivided into four groups (Sarcodina, Sporozoa, Mastigophora, and Ciliata) for medical purposes.
• Metazoa are further categorized into two phyla: Platyhelminthes (flatworms) and Nemathelminthes (roundworms).

Protozoa

• Protozoa include Sarcodina (amoebas), Sporozoa (sporozoans), Mastigophora (flagellates), and Ciliata (ciliates), each with specific characteristics and medical significance.

Metazoa: Helminths

• Metazoa encompasses Platyhelminthes (flatworms) and Nemathelminthes (roundworms).
• Platyhelminthes includes Cestoda (tapeworms) and Trematoda (flukes).
• Nemathelminthes include a variety of roundworms with differing life cycles and disease implications.

Definitions, Types of Hosts

• Definitive host: the host where the parasite sexually reproduces.
• Intermediate host: the host where the parasite develops.
• Reservoir host: a host that harbors the parasite but shows no symptoms.
• Vector: the carrier of a parasite from one host to another (often an insect).

Intestinal & Urogenital Protozoa

• Entamoeba histolytica: a protozoa that causes amebic dysentery and liver abscess.
• The life cycle of Entamoeba histolytica includes two stages: motile trophozoite and nonmotile cyst

Giardia lamblia

• Characterized by a sucking disc and a flagellated structure.
• Causes infection through ingestion of cysts.
• Produces watery diarrhea, nausea, anorexia, abdominal cramps, and flatulence lasting weeks or months; however, there is no fever.

Trichomonas vaginalis

• Causes trichomoniasis in humans.
• Characterized by a pear shape with a central nucleus and four anterior flagella.
• Exists only as a trophozoite, lacking a cyst form.
• Clinical findings in women include a foul-smelling greenish vaginal discharge accompanied by itching and burning. Male infection may be asymptomatic or induce urethritis.

Blood & Tissue Protozoa: Plasmodium

• Plasmodium species cause malaria, a dangerous disease with four species (vivax, ovale, malariae, falciparum).
• Malaria is widespread, primarily in tropical and subtropical areas (Africa, Asia, Central and South America)
• Malaria has a complex life cycle involving both mosquitoes and humans.

Toxoplasmosis

• Caused by the protozoan Toxoplasma gondii.
• Toxoplasmosis is a zoonotic disease.
• Infects a wide range of animals, including humans, but typically doesn't cause disease in them.
• Can be transmitted transplacentally in pregnant women, resulting in spontaneous abortion, stillbirth, or physically/mentally handicapped newborns.

Trypanosoma cruzi

• Causes Chagas' disease (American trypanosomiasis).
• The life cycle involves the reduviid bug (Triatoma, cone-nose or kissing bug) as a vector.
• Can lead to heart problems.

Trypanosoma gambiense & Trypanosoma rhodesiense

• Causes African sleeping sickness.
• Transmitted by the tsetse fly.

Leishmania

• Leishmaniasis is a parasitic disease.
• Caused by Leishmania spp. that are unicellular, flagellated, intracellular protozoa.
• Transmitted by female sandflies (Phlebotomus spp).
• Infection occurs mostly in the Arabian countries.
• Present in various forms: cutaneous, visceral or mucosal

Helminths

• Trematoda (flukes) and Cestoda (tapeworms) are large groups of flatworms (Platyhelminthes).
• Schistosomes, Paragonimus, and others are important trematodes, with schistosomes having the highest impact in terms of morbidity and mortality.

Nematodes

• Nematodes (also known as roundworms) are roundworms with a cylindrical body.
• They have a complete digestive tract and a highly resistant cuticle (non-cellular external coating).
• Nematodes are categorized as either intestinal or tissue nematodes, based on their location within a host.

Intestinal Nematodes

• Includes Ascaris, Enterobius, Trichuris, Necator, Ancylostoma, Strongyloides and Pinworms, and others.

Tissue Nematodes

• Includes Wuchereria, Onchocerca, and Loa, also called filarial worms owing to their microfilarial larvae presence in blood and tissue.